Turning Down the Heat

How to avoid heat-induced illnesses

On an 86-degree day in Fort Benning, Georgia, sports-medicine doctor Wade Lillegard was watching military troops ...

Photo by Luis Escobar

On an 86-degree day in Fort Benning, Georgia, sports-medicine doctor Wade Lillegard was watching military troops train when an 18-year-old recruit suddenly crumpled during a five-mile run. The young man was slurring his speech and not sweating though his temperature was 108 degrees. Suffering a heat stroke, he lapsed into a coma, awakening three days later with failing liver and kidneys and damage to his hypothalamus, a part of the brain that regulates body temperature and sweat rate. The soldier recovered but will remain more susceptible to heat illness.

In addition to heat stroke, which can not only end your race, but can cause permanent damage or even death, are less serious conditions such as cramps, dehydration and heat exhaustion.

Why Heat Hurts

Running in hot weather is not only uncomfortable, it places extraordinary stress on the cardiovascular system, because blood is directed away from the internal organs to working muscles and the skin's surface, drawing excess heat away from the core and outside the body. "The body has competing goals [cooling you down or moving you forward], so it prioritizes," says Lillegard. As a result, your heart rate increases, but your aerobic capacity decreases.